Implantable medical devices (IMDs) are well known for providing a variety of treatments. For example, implantable cardiac defibrillators are used to monitor cardiac activity, detect ventricular fibrillation, and in response to that detection, deliver appropriate therapy pulses to restore a normal heart rhythm. Implantable neurostimulators have been used to stimulate the spinal cord and brain for, for example, the treatment of chronic pain and peripheral vascular disease. Implantable pacemakers generate and apply electric stimuli in the form of pulses to heart tissue to control the timing of heart contractions.
IMDs, and other similar devices, utilize an internal power source (i.e. an electrochemical cell) to provide the power required for operation. The electrochemical cell typically includes at least an anode and a cathode. In some embodiments, the electrochemical cell includes a cathode assembly having a powdered cathode material compressed into a disk-shaped pellet and a circumferential current collector disposed therearound. The circumferential current collector increases conductivity of current to the cathode material by maintaining low resistance and exerts a sufficient hoop force magnitude on the pellet to maintain its disk shape and allow for pellet growth during discharge.
Although the above-described cathode assembly performs well when implemented in an electrochemical cell, it has certain drawbacks. For example, in some instances, the hoop forces exerted by the circumferential current collector may be too high and may cause the disk-shaped pellet to dome. As a result, the overall thickness of the cathode assembly may undesirably increase. Consequently, it may become difficult, or even impossible, to insert the cathode assembly into the electrochemical cell. Additionally, the disk-shaped pellet typically expands as the cathode assembly is discharged. This expansion may cause degradation of contact between the cathode material and the circumferential current collector and may undesirably change the overall impedance of the cell as it discharges over time. Eventually, the change in cell impedance may cause a decrease in cell capacity. As IMDs and electrochemical cells become thinner, these issues may become more pronounced.
Accordingly, it is desirable to have a cathode assembly that can maintain its original configuration over time so that it may be easily assembled into an electrochemical cell. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.